Washington: US President Barack Obama Saturday denounced the killing of an American hostage in a second failed rescue operation in Yemen, vowing to bring the killers to justice.

"The US strongly condemns the barbaric murder of Luke Somers at the hands of al Qaeda terrorists during a rescue operation conducted by US forces in Yemen in partnership with the Yemeni government," Xinhua quoted Obama as saying in a statement.

Somers, 33, a photojournalist, was seized by Al Qaeda in the Arabian Peninsula (AQAP) in the Yemeni capital of Sanaa in September 2013. Obama said he authorised a rescue operation Friday after a video released by Somers' captors announced his killing within 72 hours.

Somers was badly wounded when the US commandos reached him early Saturday, and succumbed to his injuries by the time he was flown to an American naval ship in the region, The New York Times reported, citing a senior US official.

Another hostage from South Africa was also killed in the rescue attempt, the newspaper said.

The US and Yemeni forces launched a joint mission last month to rescue Somers but failed to find him at the site, but hostages of other nationalities were present and rescued.

In a video released Thursday, the Yemen-based AQAP warned the US not to carry out any more rescue missions.

US Defense Secretary Chuck Hagel said several of AQAP militants were killed in the latest rescue mission.

The Obama administration has stepped up drone strikes on the AQAP, with a view to uprooting the group in Yemen's southern regions.